Celestia was thinking about her apprentices when Spike ran in. More specifically, she was thinking that perhaps the test of the Samsara of one hundred lives had been a little too harsh. She could remember how she justified it at the time, but in hindsight those reasons didn't seem quite enough of a justification, even if Trixie had ended up gaining new insights into illusion magic from that test.
"Princess! Princess! They have sent a message for you!"
Celestia grabbed the scroll in Spike's hands and read through it "Hmm... They are requesting the names of every member of the guard company for debrainwashing purposes. And Twilight wants me to send one of her old cardboard cutouts of herself. They've joined up with the rebellion and will try to remove Sombra in a single day."
Celestia thought about it. It was slightly reckless, but Sombra was very good at adapting when he had time to prepare, so that could be the only chance of actually completing all their missions.
She sent Spike to get the necessary papers and teleported the cutout to herself, She would not leave her apprentices hanging.
"Okay, now that we have all the names, you need to get the unicorns from the resistance to make spell papers using this plan" Twilight showed a scroll "And putting the names on the spell papers on the right parts. This should be able to free the guards."
Ranger Time looked at the scroll and thought about the plan "But who gets the spell papers?"
Twilight blushed "Ah, sorry, I forgot about that part, you should make four complete sets. Three for us and one to stay with you guys just in case."
That seemed reasonable. She looked around and saw that the other two apprentices had figured out ways to entertain themselves. Sunset was playing with a magic cube that had way more moving parts than any other she had even seen, and Trixie was putting on a small magic show.
Ranger went to give the orders to the people they had available, and when she came back, the mare saw that Twilight herself had found something to do, and was apparently teaching magic to a filly unicorn. She smiled, those three heroines that Celestia sent really made people feel at ease. Apparently, the plan was going to start two hours before sunrise(or what passed for sunrise inside the barrier anyway), so they were going to sleep soon.
She went back to organizing things.
Candity had a simple job. She just had to get close to the castle and deliver that cardboard cutout. Her night vision was good enough to go through the first part of the path, and then the eldritch lights coming from the castle did the rest of the job. When she got close enough, Candity dropped the cutout of that Twilight Sparkle unicorn. Then she watched in amazement as the thing seemed to unfold in itself and turn into more or less a normal pony, who began trotting towards the castle.
Apparently, she was going to serve as a decoy, keeping Sombra attention on the castle by tripping his alarms while the three were going to attack in the mine. It seemed simple and unlikely to go terribly wrong. They had clearly thought of everything.
Candity suddenly felt a sense of dread and started to run back to town.
In Sunset's opinion, the journey through the mine was terribly boring. Okay, Trixie and Twilight were apparently having to concentrate a lot to get through all the alarms and traps without being discovered, but Sunset really didn't have enough ability to help the two with that work, and was just "keeping watch", which pretty much meant trying not to fall asleep out of boredom. Really, when they were discovered, Sunset was mostly relieved.
She didn't really think they would be able to sneak attack the avatar of a princess, anyway.
"Who goes there? How have you gotten here without being detected?" The unicorn with a shadow cutie mark demanded to know.
She was actually rather intimidating, with a cloak that seemed to be made of living shadows, a vibrant grey coat and silver mane and a sharp helmet that seemed to be made more for intimidation than actual protection. The heavy feeling of dark magic coming from her didn't reduce her intimidation factor any, either.
Sunset could tell, Trixie had been waiting for this opportunity. She shot fireworks into the ceiling and took a pose with her forelegs to the air.
"From all over the lands of Equestria, three fillies were gathered!" She stomped the ground "Chosen among countless others for their great magical potential!" She raised her head to the sky "Trained and tested by Princess Celestia herself to follow in the footsteps of the legendary Knights of the Realm!" She did a somersault in place and created glowing plaques with the names of the three to appear above them "Sunset Shimmer, Master of the Magic Enhance! Twilight Sparkle, Master of the Magical Sign! AAAAAND... Trixie Lulamoon! Master of the Perfect Illusion!" She made the plaques explode in a shower of sparks and did a pose. Sunset and Twilight doing matching poses they had worked out during Pose Training.
There was a beat.
"What?" The avatar asked, flabbergasted.
"Not going to repeat my performance." Trixie stated sharply, then she shot a beam at the unicorn and the battle was joined.
A barrier of semisolid shadow erected itself to block the attack on the unicorn, then tendrils of darkness shot towards the three knight candidates, hoping to skewer them. Sunset did a magic-assisted jump backwards, Twilight did one of her weird teleports, wavering out of the path and Trixie vanished, revealing that had just been an illusion. Sunset took a brief moment to remember how annoying that had always been in their spars, before Twilight did her own attack.
"Soap slip!" She cried, creating a bar of soap that sped along the ground, hoping to trip the enemy.
The shadow user was surprised for a moment, but still managed to bring a tendril to spear the soap bar. That was a really versatile defence, it seemed like brute force was necessary, and thankfully that was Sunset's specialty. She quickly charged and cast a spell.
"Magic Enhance! Comet Dash!" She announced, forcefully enhancing the spell at the cost of a significant portion of her magic. But the results made it more than worth it.
The small but powerful fireball she had cast became a solid ball of earth covered in fire, and shot itself at the shadow unicorn at nearly supersonic speeds. The impact released a terrifying sound and the shadows seemed to explode, sending bits of themselves all over the area and sending the unicorn flying to the wall.
That one had always been one of Sunset's favorites.
7 years before
"Teacher! Teacher! Look what I did!" Sunset was jumping in place and waving to Celestia.
The Princess took a look at what used to be the south wall of the east wing of the palace, now a complete ruin.
"I figured out another cool spell with Magic Enhance! And if I take a little longer, I can even cast it normally!" She stop, thinking hard "But what would happen if I used Magic Enhance on that spell? I'm sure it would make an even cooler spell!" She decided with a nod.
The Princess was trembling. She must have been really proud of her student, Sunset deduced.
The avatar didn't reach the wall. With a yell, an amazing amount of shadow matter flowed out from her, forming a stretchy cushion to absorb the impact. Then she unleashed a moving wall of shadow matter directly at Sunset and Twilight. However, the purple unicorn smiled when she heard the voice she had been waiting for.
"Perfect Illusion: Mana Break!" Trixie announced, from where she was hidden directly above the enemy.
The showmare had always said the two of them made for amazing distractions to help her perform.
The unicorn avatar screamed a second after the spell hit her, her wall losing cohesion. Twilight could sympathize, Mana Break was a spell that played havoc with the body's ability to detect and manipulate its own mana, due to sending an overwhelming amount of contradictory signals. It was extremely hard to counter, though Sunset had some success simply releasing unfocused bursts of magic, so Trixie quickly teleported out of the probable blast radius.
"WAAAAAAAAAAAAAH!" Came the incredibly loud shout, and the body of the enemy shook in a grotesque movement, just before shooting out an entire rain of shadow fragments everywhere.
Thankfully, Sunset had already charged up a shield spell. It took form, a thick hexagonal shield that was also concave.
"Magic Enhance: Bunker Shield!" And the shield thickened even more, growing and gaining more facets and an additional layer.
Trixie and Twilight immediately took refuge behind Sunset, as the barrage started hitting the shield with the sound of canonballs hitting metal plates. Trixie looked to Twilight and glanced in the direction of the enemy. The purple unicorn immediately started charging the spell that would put an end to the fight. Trixie also charged up a spell of her own.
Seconds later, the barrage stopped, and the two apprentices were already waiting for it. Trixie teleported Twilight directly in front of the avatar, who was momentarily recovering from the exertion of too much magic at once, exactly the weakness of this kind of uncontrolled magic.
"May a half-life spring up from a full one..." She chanted, finishing the preparations for the spell.
"Chaos Magic: Life Divide!" The beam of the spell hit directly in the horn.
Two eyes appeared on the horn, and then a tail, and arms and finally the horn completely turned into a squirrel, which jumped away, leaving the unicorn's head bare.
After a second of silence, their opponent started becoming fainter and fainter, until she disappeared. While a normal unicorn would survive the same spell, an avatar is an entity created from magic, which can be disrupted with a large enough shock.
The three apprentices of Celestia had been successful in defeating one of Nightmare Moon's avatars.
Then, they immediately started running towards the exit of the mine, knowing that now Nightmare Moon would know she had lost an avatar, and Sombra would discover of the existence of intruders. They cast speed spells to reach the exit faster, knowing they would be able to escape before the alicorn's arrival unless she teleported. That was also why they had took the time to disable everything when coming in. And Twilight was already preparing a teleportation trap, which would at the very least give them time to get away.
From the top of the castle, a massive beam of energy shot directly towards the mine.
Trixie saw the beam of energy first, and recognized it as a forced movement spell, using the mine itself as a focus. She didn't have time to do any more than that before the spell activated.
The three unicorns got shoved right back through the mine, straight into a circular chamber, which sealed itself soon after.
Trixie saw the runes on the wall activate and recognized the unforgettable magic interference of anti-teleportation wards.
Then she felt the charging of magic energy right underneath her feet, an amount that was rapidly growing. She exchanged alarmed glances with her partners.
It seemed like the plan needed adjustment.